Data tape cartridges are commonly used for the storage of electronic data signals and typically include a metal baseplate with pins and posts extending upwardly from the base plate to support belt rollers, reel hubs, a drive roller, and tape guides. The tape alignment must be precise for the writing or reading of the desired data signals on the tape. Therefore, it is very important that the pins and posts maintain their alignment during cartridge use. This is in clear distinction to tape cassettes which merely house a length of tape on hubs that require external support for movement of tape over a tape path that is determined by external tape guides. Tape cartridges therefore are essentially self-contained machines which require precision placement and elevational orientation of internal tape guides and internal supporting pins for rotatable components.
The tape in such a tape cartridge is moved bidirectionally from one reel of tape to another reel of tape along a tape path near a forward edge of the cartridge by the action of a flexible, resilient drive belt disposed along a belt path which overlays the outer convolutes of tape on the two reels and wraps around a drive roller positioned near the forward edge. Tape cartridges of this type are disclosed in the literature (see, for example, U.S. Pat. Nos. 3,692,255 and 4,262,860). The drive roller thus serves as the intermediate coupling between a rotating capstan shaft or roller in a tape drive unit and the belt which then contacts the outer layers of tape moving between reels. The drive roller is commonly disposed near the center of the forward edge of the tape cartridge with an upper portion of largest diameter protruding from the cartridge to engage the capstan shaft or roller of the tape drive unit, and with a lower portion of smaller diameter aligned with the drive belt and forming a part of the belt path.
Several significant characteristics of the drive roller contribute to precision performance of the tape cartridge. Specifically, true concentricity of the upper and lower portions of the drive roller relative to their common central axis promotes more uniform rate of displacement of the belt, and hence of the tape, with respect to the rate of rotation of the drive roller. In addition, the drive roller may be electrically conductive to inhibit the buildup of electrostatic charge on the drive roller and drive belt. Also, the drive roller requires close-tolerance rotational and translational bearing surfaces to assure accurate alignment relative to the drive belt.
Many of these desirable characteristics for a drive roller may be readily achieved in a machined component at high unit cost, but are difficult to achieve in a molded component at substantially lower unit cost. Polymeric materials and metals are common moldable materials, but for molded components such as a drive roller having some degree of resilience, and for molding convenience and lower costs, polymeric materials are preferred because of wide diversity of available properties, and finished components requiring no further machining are produced by the molding process. However, most polymeric materials are not electrically conductive, and have a tendency to shrink and otherwise distort from precision dimensions following removal from a mold.